1. Field of the Invention
The invention relates to hand-held power tools for driving fasteners, and more particularly to hand tools including depth adjustment systems for adjustably controlling the depth to which a fastener is to be driven into a workpiece.
2. Reference to Prior Art
A power screwdriver with a depth adjustment device used to control the depth to which screws are driven into a workpiece is illustrated in FIG. 7 of U.S. Pat. No. 4,647,260 issued Mar. 3, 1987 to O'Hara et al. This depth adjustment device includes a collar that is threaded onto the housing of a power tool and a depth locator that is threaded into the collar using the same threads used to connect the collar to the housing. Ribs and ridges are formed on the collar and the locator, respectively, and are intended to restrict relative rotation between the collar and the locator to maintain the locator at a desired setting. While this arrangement generally permits an operator to maintain a depth setting when the depth adjustment device is positioned on the tool housing, unscrewing the collar from the tool housing, such as to allow tool removal for other fastener applications, causes the depth setting to be lost when the device is replaced on the tool housing. Additionally, removal of the depth adjustment device from the tool housing is time consuming since several turns of the collar are required to accomplish this task. Furthermore, since the collar is rotatable relative to the tool housing, an operator must exercise care to insure that the collar is not moved relative to the tool while adjusting the locator to a desired setting. To prevent the collar from rotating, an operator must use one hand to rotate the locator and the other hand to hold the collar against movement relative to the tool housing.
Another example of a depth adjustment device is also shown in U.S. Pat. No. 4,647,260. In this device a locator is threaded into a collar which can be snapped onto the nose portion of a tool housing. Thereafter, the locator is non-rotatably mounted on the tool housing via cooperating keys and keyways on the tool housing and the locator, respectively. Also, indexing fingers on the collar engage complementary bumps on the tool housing to maintain the collar in a predetermined angular position relative to the housing so as to maintain a desired depth setting. While this arrangement maintains a desired depth setting when the depth adjustment device is mounted on the tool housing, the setting can be lost when the device is removed from the housing since only a threaded connection exists between the collar and the locator. Thus, a desired depth setting can be lost during normal handling of the adjustment device.